the thing is that I am practicing for the ccie lab and the dynamips images does not support many of the cli commands required.hence, I am installing the iol files which can support most of the commands such below image:

L3-ADVENTERPRISEK9-M-15.4-2T.bin

Then I am uploading such images to this directory
/opt/unetlab/addons/iol/bin

and then the node fails to start message appear
Failed to start node (12)

when I upload the same to /opt/unetlab/addons/dynamips
it does not show at all in the image list when I try to create a new node.

Kindly advise me if there is a better way to practice or if I am missing anything to make it work.
Sorry for the inconvenient and thanks again for the help.